Tech Info
Manufacturing Relationships Distributing Quality….
- FLAT PRODUCTS (FLAT ROLLED PRODUCTS) : Finished steel flat products are produced from slabs/thin slabs in rolling mills using flat rolls. These are supplied in Hot Rolled (HR), Cold Rolled (CR) or in Coated condition depending upon the requirement.
- Different types of flat products are:
PLATE: Thick flat finished product of width: +500mm & Thickness: (+) 5mm which are supplied in cut/straight length. Plates are normally produced / supplied in as hot rolled condition with or without specific heat treatments.
- SHEET: Thin flat finished steel products, Width: +500MM, Thickness: (-) 5mm, Supplied in cut/straight length. Sheets are produced/ supplied in hot rolled /cold rolled/coated condition and accordingly, known as Hot Rolled (HR) Sheets or Cold Rolled (CR) Sheets or Coated Sheets.
- STRIPS: Hot/cold/coated Flat rolled products, supplied in regularly wound coils of super imposed layers. Accordingly, known as HR Strips or CR Strips or Coated Strips. Depending upon width, strips are sub-classified as wide strip or narrow strip as under :
- WIDE STRIPS: Strips of widths 600mm & above. Also known as Coils in India and Wide Coils in Europe etc. Accordingly, the terms HR Coils/ Wide Coils or CR Coils/ Wide Coils etc. are commonly used.
- NARROW STRIPS: Strips of widths less than 600mm.
- HOT ROLLED (HR) FLAT PRODUCTS are produced by re-rolling of slabs/thin slabs at high temperature (above 1000 Degree C) in Plate Mills (which produce plates) or in Hot Strip Mills (which produce strips). Hot Rolled Strips are cut into straight length to produce HR Sheets or Thin Plates.
- COLD ROLLED (CR) STRIPS are produced by cold rolling of HR Strips in Cold Rolling Mills (normally at room temperature). CR Strips are cut to produce CR sheet. CR Strips/sheets are characterised by lower thickness, better/bright finish, closer dimensional tolerance and specific mechanical/metallurgical properties. They are directly used in automobiles (cars/ scooters, motorcycles etc.), white goods, consumer durable etc. or for production of coated sheet products.
- Cold Rolled Sheets/Strips are supplied in as rolled condition (CRFH- Cold Rolled Full Hard) or in closed annealed (CRCA -Cold Rolled Close Annealed) condition or in closed annealed & skin passed/temper passed condition, depending upon the requirement of the end users.
- D/DD/IF STEEL: Specific variety of Cold Rolled Sheets/ Strips with specific chemical composition used in Tin Mills are known as Tin Mill Black Plate (TMBP).
- D/DD/IF STEEL: Specific variety of Cold Rolled Sheets/ Strips with specific chemical composition used in Tin Mills are known as Tin Mill Black Plate (TMBP).
STEEL AS PER COMPOSITION
ALLOY STEEL :
Steel which is produced with intended amount of one or more alloying elements in specified proportions to impart specific physical, mechanical, metallurgical and electrical properties.
Common alloying elements are manganese, silicon, nickel, lead, copper, chromium, tungsten, molybdenum, niobium, vanadium etc. Some of the common examples of alloy steels are:
- STAINLESS STEEL: which essentially contains chromium (normally more than 10.5% with/without nickel or other alloying elements. As the name implies, stainless Steel resist staining/corrosion and maintains strength at high temperatures. Used widely in Utensils, architectures and in Industrial applications viz automotive & food processing products as well as medical & health equipment.
Commonly used grades of stainless steels (SS) are:
- TYPE 304: Chrome – Nickel Austenitic S S accounting for more than half of SS produced in the world. 18: 8 SS used for utensils are the most common example.
- TYPE 316: Chrome – Nickel (Austenitic) SS containing 2-3% Molybdenum , intended for specific industrial use.
- TYPE 410: Plain Chromium (Martensitic) S S with exceptional strength. It is a low cost, heat treatable grade suitable for non-corrosive applications.
- TYPE 430: Plain Chrome (Ferritic) S S, offering general purpose corrosion resistance, often in decorative applications.
- TYPE 201/202 ETC. : Low Nickel Austenitic S S containing 2-5% Nickel . Used as cheaper substitute of Type 304 grade for production of utensils.
- SILICON-ELECTRICAL STEEL: which usually contains 0.6 – 6% silicon and exhibit certain magnetic properties, which make it suitable for use in transformers, power generators, and electric motors. They are normally supplied in 2 categories:
- CRGO: Cold Rolled Grain Oriented Silicon-electrical steel sheets/strips, normally recommended for use in transformers and generators.
- CRNO/ CRNGO: Cold Rolled Non-Grain Oriented Silicon-electrical steel sheets/strips, normally recommended for use in rotating machines such as electric motors.
- HIGH SPEED STEEL: Alloy steel containing tungsten, vanadium, chromium, cobalt and other metals. Depending upon composition, they are classified as Cobalt Grade and Non-Cobalt Grade. Used for manufacture of cutting tools.
NON-ALLOY /CARBON STEEL/PLAIN CARBON /UN-ALLOYED STEEL :
These steels by definition do not contain any alloying element in specified proportions (i.e. beyond those normally present in commercially produced steel in industry). Non- alloy steel is divided into 3 categories namely.
- Low carbon steel or Mild steel (normally containing up to 0.3% carbon)
- Medium carbon steel (normally containing 0.3 – 0.6% carbon) and
- High carbon steel (normally containing more than 0.6% carbon).
Non-alloy steel constitutes approx. 90% of total steel production, of which, mild steel takes the lion’s share.
SPECIAL STEEL :
Steel, in production of which special care has to be taken so as to attain the special/desired properties, such as, cleanliness, surface qualities and mechanical/ metallurgical properties.
In layman’s language, all steel other than mild steel fall under the category of special steel. But metallurgically, even mild steel/low carbon steel i.e containing less than 0.25%/0.30% carbon, may still fall under the category of special steel if any special properties is specified in the steel. Examples are DD/ EDD steel, Forging Quality steel, Free Cutting steel etc.
GUIDE TO HARDNESS TESTING OF STEEL STRIPS
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